1. Field of the Invention
The field of the invention is power generators for medical and therapeutic devices, and, more particularly, power generator control for medical and therapeutic devices.
2. Background of the Invention
The power generators for many medical and therapeutic devices, such as those used in ablative therapy, are generally remotely located from the devices. A patient cable is typically provided to electrically couple the power generator to the therapeutic device. When the length of the patient cable is long, either because of design, or because doctors or nurses extend the original length of the patient cable, the power along the patient cable can vary significantly, causing the energy delivered by the therapeutic device to be inaccurate.
In ablative therapy, targeted biological tissue is heated by a therapeutic device to create lesions. The creation of lesions in cardiac tissue, for example, is used to treat cardiac arrhythmia by preventing the propagation of electrical signals across each lesion. The energy delivered by these therapeutic devices can be in a form of ultrasound, to heat with sonic energy, radio frequency or microwave, to heat with electromagnetic field energy, or induction heating, to heat with magnetic field energy, as is known in the art. In one example, the therapeutic device includes one or more electrodes for delivering radio frequency energy. See for example, U.S. Pat. No. 6,241,724B1 and U.S. Pat. No. 6,004,269, which are incorporated by reference herein.
It is important that an accurate amount of energy be delivered to the target tissue to create the desired lesions. Delivery of less energy than expected may prevent the targeted biological tissue from being sufficiently heated to achieve the desired lesion creation. Delivery of an excess amount of energy could cause excess lesion formation.
Power loss along the patient cable may be caused by a variety of factors, including the resistance of the wire in the patient cable, the geometry of the cable (i.e., whether it is coiled or stretched), and any electrical coupling to conductive features of the surroundings, such as steel floor, pipes, and walls. The power loss could fluctuate during an operation of a therapeutic device, depending on these factors. In addition, it is a common practice to extend the length of patient cables with extension cords. The length, geometry, and electrical characteristics of the extension cords, as well as the connection between the extension cord and the patient cable, and between extension cords, could also cause power loss along the extended patient cable.
Power loss along the patient cable may become noticeable when the patient cable length reaches ten (10) feet, or sometimes even less, depending on other factors as described previously. The power loss could become significant when the patient cable length reaches about fifty (50) feet. The uncertain nature of most of the factors causing power loss discussed above (i.e., the geometry of the patient cable, the surrounding environment in which the cable is placed, and the type of extension cords) makes it difficult to calculate power variance along the patient cable. It is therefore difficult to accurately regulate the power output of a therapeutic device to compensate for the variance of the power along the cable.
It would be advantageous to be able to accurately compensate for power variance along the patient cable so that a desired amount energy is delivered to a therapeutic device connected to the patient cable.
According to the present invention, a characteristic of the power provided to a therapeutic device through a patient cable, or a characteristic of the energy delivered by the therapeutic device, or both, is sensed. A feedback signal is provided based on the sensed value to adjust the power generated by a power generatorSJ-39249.1, if necessary, so that the therapeutic device delivers a desired amount of energy.
In one embodiment, a system for delivering power to a therapeutic device comprises a generator including a power regulation circuit for producing an output power at a generator output. A patient cable is provided having a proximal end configured for coupling to the generator output and a distal end configured for coupling to the therapeutic device. A feedback apparatus is coupled to one or both of the patient cable and the therapeutic device proximate the distal end of the patient cable. The feedback apparatus is configured to sense or measure a variable that depends on a delivered power and to generate a feedback signal depending on the delivered power. The power regulation circuit controls the output power of the generator, based at least in part on the feedback signal. Methods for delivering power to a therapeutic device are also disclosed.
Other and further aspects and features of the invention will be evident from reading the following detailed description of the preferred embodiments, which are intended to illustrate, not limit, the invention.